The action potential begins at the axon hillock, a specialized region connecting the dendrite and the axon. Before the action potential may occur, an energy threshold must be surpassed. The axon hillock acts like a gateway, permitting the action potential to begin only once this minimum has been reached. From there, the action potential propagates down the axon of the neuron. This is the long, tail-like extension of the cell which connects to the dendrites of other neurons. At the end of the axon are the terminal buttons. It is here that neurotransmitters are released from the neuron, which travel across the synaptic cleft to bind to neighboring dendrites of other neurons. If these dendrites receive sufficient excitation, then they will release their own action potentials, and repeat the process; thus, the action potential sends information between nerve cells.

The correct answer is that dendrites are the sole receiver of stimulation because the soma of the neuron can also receive input from other cells. The other answers were wrong because they are true characteristic of the nervous system. Summation can be temporal or spatial depending on the amount of cells communicating with the neuron. One pre-synaptic cell can send input to the neuron multiple times to result in temporal summation, and multiple cells can send input to the same cell resulting in spatial summation. The total amount of input received by the dendrites and soma will sum in the initial segment of the axon, if the axon reaches the depolarization threshold, voltage gated sodium channels will open and set off a chain reaction that propagates the action potential to the axon terminal. This process is faster in cells with myelin because less of the axon needs to be stimulated to send the action potential to the terminal due to the insulation of segments by the myelin.

The correct answer is voltage gated sodium channels. These cells are in the axon of the neuron and are only opened when the cell reach the depolarization threshold. Voltage-gated potassium channels are responsible for the re-polarization of the cell or the hyper-polarization. Voltage-gated calcium channels are apparent in the axon terminal of the neuron and play a role in the release of neurotransmitters. Sodium channels and potassium channels are in the dendrites and soma of the neuron. They interact to keep the cell at it's resting potential and inputs to the cell can affect the amount of sodium or potassium entering the cell. This can lead to the cell becoming depolarized or hyper-polarized, but do not themselves lead to the surge of activity that generates the action potential.

An action potential describes the event of an electrical impulse being activated by a given neuron once it is sufficiently polarized. We may think of an experience such as pain. If I prick my finger with a needle, I feel a small amount of pain. If, however, I unfortunately lose my fingertip due to a mechanical accident of some sort, I will feel much more pain. This difference in pain is not due to the strength of any one given action potential. An action potential either leads to an electrical impulse or it does not (in other words, it is all-or-none). There are no gradients in strength or degree; however, the number of action potentials occurring across neurons can have a cumulative effect (e.g., greater number of nerve cells involved in the more serious injury of losing a finger tip equates to a greater experience of pain).

The "soma" is the name for the cell body of a neuron. This refers to the part of the neuron that houses the cell nucleus, and other organelles necessary for the life of the cell. This region is distinct from the dendrites, which are the branch-like structures that protrude from the soma. It is also distinct from the axon, the long tail-like structure which extends away from the cell body. "Myelin" is the name of a fatty substance which coats the axons of some nerve cells in order to insulate them. "Nerve" is a word that may be used interchangeably with 'neuron', particularly when referring to those in the peripheral nervous system. However it is not an alternate name for the cell body_._

The tiny space between a synapse of one neuron and the synapse of another is called the synaptic gap. It is also known as the synaptic cleft. It is in this space where neurotransmitters can be exchanged between neurons. It is important to note that not all neurotransmitter molecules emitted by a given synapse or necessarily received by the synapse across the synaptic gap. Multiple variables are at play. The gap is not needed for the neurons to have space to grow nor is the brain kept moist via these clefts.

Myelin is a fatty coating that develops around the axons of some nerve cells in order to insulate them. This insulation serves to aid in the completion of action potentials. Glial cells exist in the brain, and aid in nourishing the neurons. Myelin does not serve this purpose. Myelin also does not protect against viral attack, nor that of other pathogens. Although myelin insulates the cells, it is not capable of speeding their rate of firing. Finally, myelin has no interaction with neurotransmitters, and does not increase the receptivity of a nerve cell to stimulation.

While potassium—alongside sodium—plays a vital role in the functioning of neurons and in the exchange of neurotransmitters, it is not a neurotransmitter. Rather, it is involved in the shifting of polarity in the neuron that leads to an action potential. In other words, the amount of potassium present in a given neuron directly impacts meeting the threshold of an action potential. Serotonin, dopamine, and norepinephrine are neurotransmitters released by these action potentials.

Sodium and potassium are crucial in the stages of the action potential. This is due to the fact that by controlling the concentrations of these positively charged ions within the cell, an electrical gradient may be effected across membrane of a neuron. By actively pumping sodium ions out of a cell, a neuron maintains a negative resting potential of approximately -70mV. During the action potential, ion channels open to allow sodium to flood into the cell along the direction of this electrical gradient. This in turn allows the propagation of the nerve impulse down the length of the axon, as positive ions activate more ion channels, not unlike a chain of dominoes. By subsequently controlling the concentration of potassium ions, and pumping sodium out of the cell, membrane resting potential is restored, allowing for the process to repeat itself once sufficient excitation is reached. Calcium ions have a role in the action potential as well, but it is much more specific, and limited to the release of neurotransmitters at the end of an action potential. Nitrogen and chlorine do not have crucial roles in the nerve impulse.

The nerve impulse within a neuron is primarily an electrical event. This is due to the fact that the cell becomes polarized and then proceeds through rapid depolarization and repolarization during and following the action potential. All of this is achieved through electrical gradients, which are maintained across the cell membrane in order to create potential energy. Communication between neurons, on the other hand, is achieved through the transmission of chemical information. Neurotransmitters released from the terminal button of one neuron cross the syaptic cleft to bind to receptor sites on neighboring dendrites of other nerve cells. The transmission of these chemicals delivers information, leading to excitation or inhibition of the receiving cells. "Axon and dendrite" does not correctly describe this relationship. "Neurotransmitter and action potential" seems more appropriate, but these two items are in the incorrect order to describe nerve impulse and interneuronal communication, respectively.